The invention relates generally to an apparatus and method for delivering and deploying an expandable prosthesis within a body canal.
Prostheses for transluminal implantation in body canals, such as blood vessels, for repair or dilation are known in the art. These prostheses may be tubular elements which are non-extendible or extendible (i.e. adapted to extend longitudinally), or they may be self-expanding in the transverse direction or expandable in the transverse direction by a dilation balloon. A typical self-expanding stent is disclosed in U.S. Pat. No. 4,655,771 to Wallsten. The stent has a radially and axially flexible, elastic tubular body with a predetermined diameter that is variable under axial movement of the ends and which comprises a plurality of individually rigid but flexible and elastic wire elements defining a radially self-expanding helix. This type of stent is known in the art as a xe2x80x9cbraided stent.xe2x80x9d
Another stent, which has particular applicability to the present invention is disclosed in U.S. Pat. No. 5,545,211 to An et al. This stent has a greater tendency to resist foreshortening. It also has a significantly improved hoop strength which it is believed provides more radial force for maintaining the patency of a vessel lumen. As a consequence, this stent tends to resist compression.
A typical stent delivery device comprises a catheter assembly having a tubular sleeve with a self-expandable stent placed in contracted condition within a distal area of the sleeve. The sleeve is positioned by means of a guide wire and an introducer. The device further includes a means to expose the stent by sliding the sleeve away from the stent. The device can be directed to the site of implantation where the stent is released from the sleeve and implanted into the body canal.
One of the problems related to the placement of self-expanding prostheses such as stents is that they are highly compressed within delivery catheters to permit them to be maneuvered within the vascular system. The compressive forces necessary to reduce the stent have been found to lead to excessive friction between the stent and sleeve during deployment from the delivery catheters. Excessive friction may be particularly noticeable for stents which provide relative large radial forces for maintaining the patency of a body canal, such as the stent disclosed in U.S. Pat. No. 5,545,211 In addition, visualization of a compressed stent within the catheter is problematic, particularly when the stent must be placed near a branching body canal. Currently, hand held devices with pivoting levers have been utilized to provide the necessary forces to deploy the stent. Deployment of the stent at the desired location sometimes involves the process of partially deploying the stent and determining whether the stent is properly located in the vessel. The deployed portion of the stent may expand and impinge against the internal wall of the body canal. If the stent is improperly positioned, the stent may have to be recompressed and recaptured within the sleeve before moving it to a new location because friction between the stent and body canal would otherwise prevent movement of the prosthesis and/or because the body canal may be damaged by sliding the stent against the internal wall of the body canal. In some cases, it may not be possible to recompress and recapture the stent within the sleeve if the stent provide large radial forces for maintaining patency of a body canal.
Thus, there remains a need for a delivery device that is capable of partially deploying a stent and thereafter repositioning the partially deployed stent. There is also a need for repositioning a stent without having to recapture the stent within the sleeve. And, there is a need for partially deploying a stent having a high compressive force and repositioning such a stent.
In accordance with the present invention, a delivery and deployment apparatus is provided that is capable of partially deploying a stent and thereafter repositioning the stent without having to recapture the stent within a sleeve. The system of the present invention further permits the sleeve to be partially withdrawn and the delivery catheter to be repositioned without excessive frictional engagement with the body canal. The invention has particular applicability with a stent having a high compressive force, since the device of the present invention does not require recompression of the stent and recapture within the sleeve. Furthermore, the delivery apparatus actually utilizes the stent""s compressive force to its advantage in that repositioning of the stent relies on the column strength of the partially deployed stent to accurately reposition it.
In accordance with an illustrative embodiment of the present invention, the delivery apparatus comprises an elongated sleeve having a proximal end and a distal area with a distal end. A self-expandable prosthesis is placed in contracted condition within the distal area. An outer shaft is disposed within the sleeve and movable relative to the sleeve. A securing member is disposed on a distal area of the outer shaft, and a distal area of the prosthesis is secured to the outer shaft by the securing member. The delivery apparatus may further include an inner shaft which is disposed within the outer shaft and movable relative to the outer shaft. A tip is disposed at a distal end of the inner shaft and includes at least one side port for bleeding contrast medium adjacent to the atraumatic tip. The inner shaft may further include a lumen for receiving a guide wire.
The delivery apparatus may be operated in the following manner. The prosthesis is compressed and loaded into the distal area of the sleeve. The outer shaft is positioned within the prosthesis and sleeve, and the distal area of the prosthesis is secured to the securing member. Via the distal end of the outer shaft, the inner shaft is passed through the outer shaft until the atruamatic tips abuts against the securing member, thereby lockingly securing the prosthesis. With the prosthesis properly positioned within the body canal, the prosthesis is deployed by causing a longitudinal motion between the sleeve and outer shaft to expose the prosthesis and by releasing the securing member from the distal area of the prosthesis. If the prosthesis requires repositioning, retraction of the sleeve is terminated prior to releasing the prosthesis from the securing member. The prosthesis is then repositioned, the sleeve is fully retracted, and the prosthesis is released from the securing member.
Other objects, features, and advantages of the present invention will become apparent from a consideration of the following detailed description.